Analysis of the induction of chlorophyll fluorescence in leaves and isolated thylakoids: contributions of photochemical and non-photochemical quenching

Abstract

Quantitative analysis of the changes in the reduction-oxidation state of photosystem 2 electron acceptors and excitation energy distribution between photosystems 1 and 2 during the induction of chlorophyll fluorescence at 685 nm from a minimal to a maximal level in dark-adapted leaves and isolated thylakoids from Pisum sativum are presented. The data show that changes in the fluorescence yield during the induction phase are attributable not only to changes in the probability of trapped excitation energy being used for photosystem 2 photochemistry, as previously predicted, but also to large changes in the probability of energy loss through non-photochemical processes. A significant and variable amount of fluorescence quenching by non-photochemical processes in both leaves and thylakoids is demonstrated. The non-photochemical quenching of fluorescence during induction in isolated thylakoids was not modified by addition of a range of ionophores, which effectively destroyed delocalized electrical and cation concentration gradients across the membranes. Significant quenching of fluorescence by non-photochemical processes was also observed in both leaves and thylakoids treated with 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea.